docs: def save(self, p_todolist):
          """
          Saves a tuple with archive, todolist and command with its arguments
          into the backup file with unix timestamp as the key. Tuple is then
          indexed in backup file with combination of hash calculated from
          p_todolist and unix timestamp. Backup file is closed afterwards.
          """
          self._trim()
  
          current_hash = hash_todolist(p_todolist)
          list_todo = (self.todolist.print_todos()+'\n').splitlines(True)
          try:
              list_archive = (self.archive.print_todos()+'\n').splitlines(True)
          except AttributeError:
              list_archive = []
  
          self.backup_dict[self.timestamp] = (list_todo, list_archive,  self.label)
  
          index = self._get_index()
          index.insert(0, (self.timestamp, current_hash))
          self._save_index(index)
  
          self._write()
          self.close()